1. Field of the Invention
This invention relates to drumheads composed of multiple plies of synthetic resin films.
2. Description of the Related Art
In general, drums are made of hollow cylinders whose openings are covered with stretched skins, that is, drumheads. In particular, drumheads composed of synthetic resin films can be manufactured at relatively low cost and are therefore advantageous in mass production in comparison with drumheads composed of natural leathers. In addition, synthetic-resin drumheads are hardly influenced by environmental factors such as variations in temperature and humidity. Furthermore, they produce relatively “hard” sounds and are characterized in that tone pitches and tone colors are difficult to be varied. Generally, synthetic-resin drumheads are each composed of one or two plies of synthetic resin films. Drumheads each composed of a one-ply synthetic resin film are characterized in having good responses and are capable of producing sound components of higher frequencies. There may be provided three types of drumheads, each composed of two plies of synthetic resin films, as follows:                (1) Two synthetic resin films are merely disposed one over the other.        (2) Two synthetic resin films are joined in such a way that outer peripheries thereof are adhered to each other by adhesive while center portions thereof are brought into close contact with each other.        (3) Two synthetic resin films are joined in such a way that the entire areas thereof are completely adhered to each other by adhesive.        
In addition, it is possible to paint patterns on surfaces of films, which contribute to variations in sounds produced by drums.
In conventional drumheads, each composed of multiple plies of synthetic resin films that are laminated together and are merely brought into close contact with each other, when small amounts of air remain between films in the manufacture of drumheads, the entire areas of the films cannot be brought into complete close contact with each other, which may cause unwanted loss in transmission of vibrations that occur when drumheads are beaten by drumsticks and the like. There is a problem in that unwanted variations may occur in sound qualities in drums; therefore, it is very difficult to manufacture drumheads having stable sound qualities.